So basically Gross' fund at Janus, which has seen assets swell from just $13 million when Gross joined the firm in September to more than $1.2 billion as of November 30, according to data from Janus, grew because he put a bunch of his own money it.

Here are Grind and Zuckerman:

"The investor inflows into the Janus Global Unconstrained Bond fund in October and November were critical because they helped push the fund past $1 billion in assets under management, a key threshold for large investors, according to investors and analysts. Despite Mr. Gross's star power, some large pension funds and their consultants have said they couldn't previously consider his fund because of its small size."

And so you could say Gross is investing in his own fund because, well, it's his own fund and that seems like the kind of thing someone might do. But by putting a bunch of his own money into the fund — Gross' net worth is estimated at $1.9 billion, according to data from Bloomberg — it passes an AUM threshold that could've been holding back potential investors.

Which is great for Gross, the fund, and Janus Capital.

Presumably as an investment professional, you're confident in your own ability to get returns. Additionally, putting a bunch of your own money into a fund you manage acts as a show of confidence to prospective investors, as you now have what is referred to as "skin in the game." When the fund loses money, you personally lose money, creating an incentive to not lose money. (Like, there is the whole thing about being a fiduciary and so on, but people break those rules all the time.)

When you don't run a lot of money, it's hard to get people to invest with you, even if you're Bill Gross.

Note, again, the last sentence of the excerpt above: "Despite Mr. Gross's star power, some large pension funds and their consultants have said they couldn't previously consider his fund because of its small size."

And so now, due to his own capital injection, Gross' fund at Janus quickly bypasses the hardest part of starting a new fund: capital accumulation.

When Gross joined Janus, the Unconstrained Fund had just $13 million in assets under management, and resulted in this ridiculous chart which compared to the more than $200 billion he used to manage at PIMCO.

But now the Unconstrained Fund has more than $1 billion in assets under management, opening it up to newer, bigger investors in just months, even if Gross had to do a bunch of the legwork himself.